#include <stdio.h>
int main ()
{
	float sum=0.0,mark=0.0;
	int numbers_of_students=0;
	while(mark>=0)
	{
		printf("Please enter students mark \n");
		scanf("%f",&mark);
		if (mark>100||mark<0)
			continue;
			sum+=mark;
          numbers_of_students++;
	}
	printf("mark is %.1f\n",sum/numbers_of_students);
return 0;
}